Bit for boring long holes



March 25, 1930. E. MUHLHOFF BIT FOR BORING LONG HOLES Filed April 22, 1929 n w, n m U Patented Mar. 25, 1930 EDUABD I'U'HLHOFF, OI BEMSCHEID, GER-MANY, ASSIGNOR TO FIRM PETER FBIEDB. MUHLHOFF, WEBKZEUGFABRIK, F BEMSCHEID, GERMANY IBI'I FOB BO RING LONG HOLES Application filed April 22 1929, Serial No. 857,276, and. in Germany September 20, 1928 In bits for boring long holes as heretofore known the cuttingedges and the bit body are subjected to an extraordinarly high strain. As a result it frequently happens that the cutting edges become broken or the bit body itself breaks.

The present invention aims to relieve these difficulties, and to accomplish this end at least one of the cutting elements of the bit is provided with notches, teeth, or the like. This element thus cuts tooth-like grooves in the material to be bored, the projections of which are then pared off by the following cutters of the borer. Thus the strain is considerably reduced, and likelihood of breakage is minimized.

For illustration, the invention is shown in the drawings in a form more especially designed for borin wood, whereof:

Fig. 1 shows a it with two cutting edges, or cutters;

Fig. 2 of Fig. 1.

In the exemplary embodiment illustrated in Figs. 1 and 2, the bit a is provided with a saw-tooth-like cutter b and a smooth cutter 0. Upon rotation of the bit in the bore hole the cutter b bites a series of grooves in the wood, the cross sections of which correspond to the shape of the saw-tooth-like cutter, so that tooth-like formations result in the wood, the pro'ections of which can be readily removed y t e unbroken smooth cutter c.

As is clearly shown in the drawings the cutting edges are properly relieved by backing ofi their rear sides, and the cutters have an appreciable rake, these features being clearly shown in Fig. 2 and being well understood in the art.

It will be appreciated that the embodiment shown provides the maximum space between the cutters to receive the relatively large chips. As many as four cutting blades, spaced 90 apart, can be used and still maintain a suflicient chip receivin space for many shows a section taken on line w--a:

t pes of work, but the embo iment compris 1 ing but two blades, as shown, the best.

It is obvious divide the cutters in is thought to be that the notches which subthe manner described of cutting edges arranged longitudina may also be used in other forms of bits for boring long holes, as for example, those havmg twisted grooves, whereby a similar improved operation may be obtained. I accordingly do not desire to be limited to the specific embodiments shown and described, but define m invention by the following claim.

Vhat I claim is:

A bit for boring long holes comprising a shank and a relatively long working portion provided with two distinctly different types 1 thereof, spaced circumferentially at least 90 and comprising, respectively, a preliminary notching or chip dividing means and afinish cutter, sald notching or chip dividing means being made up of a pluralt of relieved serrated teeth having percepti le rake and said finrsh cutterbeing made up of a continuous relieved, smooth cutting edge, so that strain on the cutting edges and working fportion of said bit and conse uent dan er 0 b k thereof will be redi lced. g ma age In testimony whereof, I have signed my name to this speification.

UARD MUHLHOFF. 

